The study of twins / Peter Mittler.

  • Mittler, Peter J.
Date:
[1971]
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The study of twins / Peter Mittler. Source: Wellcome Collection.

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    27 Medical and scientific studies Thorndike (1905). He used a mixed battery of 'intelligence' and attainment tests, including tests deliberately designed to measure formal training, such as addition and multiplica¬ tion, and others which, he assumed, were less affected by formal training, such as word opposites, misspellings and serial cancellation tasks. He found that within pair correla¬ tions were the same for 'trained' as for 'untrained' functions, and therefore concluded that 'the similarity of twins was in¬ herent rather than acquired'. This conclusion was reinforced by a second finding that the correlations for older twins were slightly lower than those for younger twins; Thorndike argued that if environmental factors were important in creating similarity, they should become greater as the child became older. The first study which systematically compared twins with other children was that of Merriman (1924) who used the 1916 version of the Stanford-Binet Scale, as well as the Army Beta and the National Intelligence Scale, and also collected teachers' estimates of intelligence. Although he was mainly concerned with comparison of identical and fraternal twins, he also tabulated the distribution of IQs of the entire group of twins. The mean IQ of his twin groups was only ninety-six but he concluded that twins suffered no intellectual handicap, and attributed the lower mean score to selection effects. Following these early studies, twin research was con¬ ducted intensively in many countries. This will be reviewed in later chapters, but it is important to stress that many disciplines other than psychology make use of the twin method; in particular, epidemiological studies of health and morbidity have made an important contribution to medical knowledge. The World Health Organization (1966) has pub¬ lished a register of twin studies from which it is clear that twin research is actively carried out in many countries, es¬ pecially the USA, the Scandinavian countries and Japan. The many topics listed by WHO range from alcoholism to rheumatic diseases. Much research is now devoted to refin¬ ing measures of zygosity determination, and to the varia-